docs: def concatenated(fp):
          """Read lines from fp concatenating on backslash (\\)"""
          line_parts = []
          for line in fp:
              line = line.strip()
              if line.endswith('\\'):
                  line_parts.append(line[:-1].rstrip())
              else:
                  line_parts.append(line)
                  yield ' '.join(line_parts)
                  line_parts[:] = []
          if line_parts:
              # Impossible:
              raise RuntimeError("Compiled file ends with backslash \\")